MOSCOW — An explosion rocked an international terminal of Moscow’s busiest airport on Monday afternoon. There were conflicting reports on the number of dead and injured. The authorities were seeking to determine the cause.

Moscow police were put on terror alert, the RT television station reported.

Russia’s Interfax Agency reported that the blast in the airport, Domodedovo, killed as many as 10 and left many more injured. Russia’s Investigative Committee said there were at least 20 casualties, without differentiating between injured and dead. News reports citing anonymous officials said at least 10 people had died. The Health Ministry reported that 130 had been injured.

Russian news agencies, citing witnesses, said airport halls were filled with smoke, so much so that it was difficult to count the number of dead. International arrivals were being diverted to nearby, according to local media reports.

The explosion occurred at 4:32 p.m. local time, according to RT television.

The airport, southeast of the capital, is Russia’s largest hub for international travelers, with more than 20 million passengers passing through last year.